Snap switch



G. O. WlLMS SNAP SWITCH Oct. 28, 1941.

Filed 001:. 19, 1938 2 Sheets-Sheet l THEOUGH MEMBER 50 mm m Wm m G. O. WILMS SNAP SWITCH Oct. 28, 1941.

Filed Oct. 19, 1958 2 Sheets-Sheet 2 .JEPII.

I .lIlul.

INVENTOR. wzw/ 0 40m Patented Oct. 28, 1941 SNAP SWITCH Gustav 0. Wilms, Milwaukee, Wis., assignor to Allen-Bradley Company, Milwaukee, Wis., a corporation of Wisconsin I Application October v19, 1938, Serial No. 235,760

14 Claims.

This invention relates in general to a snap switch and more particularly to a snap switch utilizing a combination of springs operable to move a contact back and forth from one position to another position.

An object of the invention is to provide a snap switch of simple construction and design, the contacts of which are definitely and rapidly opened or closed, even though a slow moving force is applied to the actuating mechanism of the switch.

Another object is the provision of a snap switch which uniformly and consistantly responds to prescribed actuating force or displacement.

Another object of the invention is to provide a switch in which the operating characteristics of the snap action elements may be accurately achieved without requiring precise adjustments during assembly thereof.

A further important object of the invention is the provision of a switch adapted to operate with a minimum of friction and that of practically constant degree.

Another object is the provision of a snap switch, the contact carrier of which is a flat spring unstressed before assembly.

A still further object is the provision of a switch having an actuatable means comprised of fiat spring material to which resilient properties are imparted while the material is held in a predetermined form.

With the above and other objects in view which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

In the accompanying drawings;

Fig. 1 is a side elevational view, partly in section, of the contactor element and associated parts;

Fig. 2 .is a similar view showing the switch parts with the contactor element in an alternate control position to that of Fig. 1;

Figs. 3, 4 and 5 are diagrams of the forces involved in a cycle of operation of the contactor element in a stable position, in a position approaching instability and in a second position of stability, respectively.

Fig. 6 is a graph'of the action and reaction said element being in the form of a punching from a piece of flat spring material.

Referring more particularly to the accompanying drawings, a preferred embodiment of the invention is shown. In the drawings there is shown a contactor element designated generally by the reference character I, said element comprising a punching of fiat spring material having a cutout forming a contact carrier arm 2, and an inner spring arm 3, said arms emanating from a common base 4. The cutout is substantially U-shaped with the legs terminating in the base 4, thus defining the spring arm 3 in the form of a blade disposed within the contact arm 2, and having its outer free end 5 spaced an appreciable distance from the inner edge 6 of the contact arm 2. The edges 5 and 6 are provided with centrally aligned, oppositely disposed tips I and 8, respectively.

The contactor element as used in a switch wherein it is desired to return to a standing position on removal of the operating force is constructed as shown in Fig. 11; with the inner spring arm 3 forming a slight angle with the plane of arm 2; On the other hand if it is desired that the switch remain in either of two positions independent of the operating force, the contactor element is formed as in Fig. 11 with the exception that the inner spring arm 3 is constructed to lie in the same plane as arm 2.

Interposed between th edges 5 and Ii, of the arms 3 and 2 respectively, is an expansion spring I0 provided with cup-shaped end caps II and I2, said caps having a central internally formed conical depression which function as pivot seats for the tongue members I and B. The spring II) causes the arms 2 and 3 to spread out of longitudinal alignment to the extent of producing a substantial flexure in the spring arm 3 in a direction away from the main longitudinal axis of the contactor element I. It is significant to note that the arms 2 and 3 are so constructed as to forces involved in a cycle of operation of a switch e c pable of passing through the longitudinal carrier planes of one another in passing to alternate operating positions.

To limit the normal deflection of the arm 3 and at the same time insure against derangement of the expansion spring I0, there is provided a stop |3 against which arm 3 comes to rest. The arm 2 carries on its free end oppositely disposed contacts l4 and I which are adapted to engage and disengage stationary contacts 5 and II, the latter constituting control positions between which the contact arm 2 is oscillated in the functioning of the switch mechanism.

It is obvious that the mechanism of this invention may be embodied in many different types of commercial structures. For the purpose of i1- lustration, in addition to uses where the switch is manually operated, the switch mechanism as shown herein, may be associated with various kinds of control devices, such as those which set up actuating forces in response to changing pressure, temperature, chemical composition, or mechanical displacement. Regulation of such conditions may then be secured by inclusion of the switch of this invention in an electric circuit organization or system designed to balance, restore or regulate such conditions.

Referringto Figures '7, 8, and 9, the switch mechanism per se is shown mounted on a moulded panel 2|), having an abutment 2| centrally located with respect to the longitudinal axis of the panel and adjacent one end thereof. Upon this abutment the contact element is flexibly supported in cantilever fashion by riveting or otherwise suitably securing the base 4 of said element to the abutment 2|. Inasmuch as the arms 2 and 3 of the contactor element I are formed of spring material and have their mounted end rigidly anchored to the abutment 2|, rubbing friction at this point is reduced to a negligible and consistent quantity. This is an important feature from the standpoint of uniformity of operation, since the force required to actuate the movable switch parts of this invention is a small quantity and remains constant.

On the other end of the panel 20 there is formed a pair of spaced oppositely disposed abutments 22 and 23 on which are mounted the stationary contacts l6 and II, respectively. The space between the abutments 22 and 23 accommodates the end of the contactor arm 2 so as to permit the contacts l4 and I5 carried thereby to alternately engage and disengage stationary contacts l6 and I1. Each of the contacts l6 and I! may be supported by L-shaped bracket members I9 and I9 riveted to the abutments 22 and 23 respectively and provided with terminal screws 24 to which suitable conductors may be connected.

A relatively stiff L-shaped member 25 is secured to the abutment 2|, in electrical contact with the contactor element I, and is provided with an arm 26 overlying the spring arm 3 so as to serve as a stop for the outward movement of said spring arm. The short arm 21 of the member 25, is provided with a terminal screw 28, and when the switch is connected in an electrical circuit this terminal is common to the control contacts I6 and I1.

A pressure responsive actuating plunger 30, reciprocally mounted in the panel 20 and having an external head or button 3|, is adapted to be placed in direct pressure receiving relation with any actuating means either mechanical or manual (not shown). The head 3| being of larger diameter than that of the aperture made in the panel 20 for the accommodation of the plunger 30, limits its inward movement, and a split resilient ring 32 seated in an annular groove formed near the inner end of the plunger 30, prevents the dislocation thereof. The end of the plunger 30 is provided with a rounded or spherical shaped projection 33 adapted to have substantially a point contact with the spring arm 3 at a position substantially central on the flat surface of said arm. The normal spacing of the plunger 30 from the arm 3 is preferably such that the free end of said arm comes to rest upon the stop l3 with the projection 33 only slightly separated from said arm. This arrangement provides for only a slight travel of the plunger 30 in contacting with the spring arm 3 when moving inwardly under the influence of an actuating force.

The distance of point of contact, of the projection 33 with the arm 3, from the abutment 2|, is of considerable importance. For instance, if the plunger 3|), is located too near the free end of the arm 3, the latter will have little, if any, resiliency as compared to that obtained by locating the plunger closer to the point of support of the arm 3. For that reason it is preferable to have the plunger 3|) located close to the abutment 2 I.

If it is desired that the switch be biased so as to return to its initial position on removal of the operating force, spring element shown in Fig. 11 is used. In such case the actuating force or pressure applied to the plunger 30 must be applied and maintained, and it is obvious that the length of the plunger should be suflicient to maintain contact with the spring arm 3 to not only effect the snap action thereof, but also to retain the arm 3 in its snapped-over-position against the bias of said spring in a reverse or opposing direction.

The switch may be'cooperatively positioned with respect to a thermo-responsive bellows or similar actuating device, by inserting screws in apertures 34 diagonally positioned on the panel 20. The attachment of the switch 2 to the actuating device is of a permanent nature and in that respect the unit may be readily incorporated with a variety of devices that may be operated thermostatically with or without the use of a volatile fluid.

In the event a switch is desired which shall remain in either of two positions a spring element modified with respect to that shown in Fig. 11 is used in which arms 3 and 2 are in the same plane or nearly so. In this case a manual reset member may be used which is similar to member 30 and mounted to operate in the reverse direction.

With reference to the contactor element as shown in Fig. 11 and within the scope of this invention the arm 3 may be made as a separate piece and the arm 2 in a U-shaped form in another separate piece. With this construction these two separate pieces may be clamped together at 4, to form the equivalent of the spring shown in Fig. 11.

The material and the treatment of the material of which the contactor element is made are important factors in the present switch construction. The contactor element I may be punched from a number of sheet materials, but I prefer to use beryllium copper alloy, which is commercially available. One composition which I have found quite satisfactory contains about 2.25% beryllium and about 97.75% copper.

The spring arm 3 as shown in Fig. 11 is in clined to the longitudinal axis of the contact arm 2. In forming this element from beryllium copper alloy, spring arm 3 may be so flexed and while held in that position in any suitable manner as by clamping, the element I is subjected to the well known heattreatment for this alloy called precipitation hardening, or age hardening which treatment imparts a permanent set or angular bend to the arm 3 as well as the necessary resiliency. In the event that a contactor element is desired wherein arms 2 and 3 are in the same plane, the process of treatment is the same except that the contactor element, during heattreatment, is kept flat as by clamping between two parallel plates.

Having described the construction of my switch, I will now describe the operation of the elements thereof. In so doing resort will be made to an analysis of the stresses involved, and to graphs and diagrams thereof shown in Figs. 1 to 6 1nclusively. It is assumed that the switch is being actuated by an actuator capable of exerting a force sufficient to eifect the snap action of the switch mechanism, and that this force is applied to the plunger 30. In the present analysis, the forces involved atv the pivots which are the seats formed in the cup members II and I2, will be referred to as pivotal forces."

Fig. 1 illustrates the contactor mechanism in passing from a stable to an unstable or critical position from which the contact carrier will snap to its alternate control position shown in Fig. 2.

In this case the spring element is of the self returning type as shown in Fig. 11.

The diagrams of Figs. 3, 4 and 5 show the resolution of the principal forces which come into being with the operation of the switch. In these figures the force Fs represents one pivotal force. Its components resolved perpendicular and parallel to the longitudinal axis of contact arm 2 are shown, and are marked Fn and F7), respectively. The opposing or balancing force due to the spring I 0 is Ss, and its components resolved perpendicular and parallel to the longitudinal axis are shown and marked Sn and S17 respectively. Under static conditions, the forces Sn and Fn as well as Fp and Sp are equal and opposite.

As the force F applied through member increases, the arm 3 is flexed and Fs increases slightly and the direction of Fs is altered, becoming more nearly parallel to the longitudinal axis. Consequently, Fn and Sn decrease. As the position of instability is approached, a position such as shown in Fig. 4 is assumed. In this position, Fn and. Sn are still equal, and any further decrease in Fn due to displacement of point 1 toward the left, results in a decrease to zero and then a negative increase in Sn which grows beyond and over-powers Fn and consequently the switch spring 3 moves to a new position of equilibrium as shown in Fig. 5.

The foregoing action can be more clearly explained by an examination of Fig. 3 and the curve of Fig. 6.

It will be noted in Fig. 3, all pivotal forces and their components are shown and are as follows: S's equal and opposite to Ss, Sp equal and opposite to Sp, F'n equal and opposite to Fn, F's equal and opposite to Fs, F'p equal and opposite to Fp, and S'n equal and opposite to Sn.

In Fig. 3, F0 is the contact pressure, the value of which is determined by the magnitude of S'n. Sn is, of course, equal and opposite to Sn, which is also equal to Fn, when the switch is in static equilibrium. Consequently, it is sufficient, except for frictional forces, to discuss variations in Fn and Sn when describing the performance of the switch.

In Fig. 6 the forces Fn and Sn are plotted in superimposed curves as functions of the "displacement of spring which vis the displacement of point I on the member 3.

Sn follows a relation shown in the solid line curve of Fig. 6. This force varies non-linearly with respect to displacement of the point 1, whereas the force Fn while following Sn up to a certain point varies very nearly linearly with respect to displacements of point 1 over the remaining part of the curve. Thus, as'the arm 3 is displaced by an increase in F applied through member 30, the point 1 assumes successive positions corresponding to points N and P on the solid curve of Fig. 6. At points N and P which correspond respectively to Figs. 3 and 4 the force Fn in both cases is equal to Sn. The switch is therefore in a stable condition.

At a displacement represented by P, further increase in the displacement of point 1, due to an increase in F, results in Fn exceeding Sn for any displacement of point I between the point P and the point Q on the curves and Fn is therefore plotted on the dotted line.

At position Q, Sn has changed sign and consequently the contact pressure will be reversed as shown at Sn in Fig. 5. It will be noted that point P which is the position approaching instability, occurs at a displacement of point I at which Sn is positive. Thus, if the frictional forces plus Sn are smaller than Fn at slightly beyond this point P, the contact pressure Fc cannot go to zero under equilibrium conditions prior to reversal of the switch.

It is assumed in the diagram of forces shown in Figs. 3, 4, 5 and 6 that the contact element I is coplanar and not selfreturning.

It is to be noted that one advantage of this invention is that the flexible spring 3 during preliminary stages of actuation stores up energy which is later effective to operate the switch.

In the embodiment of my invention as shown, the arm 2 being made of spring material is resilient and is slightly flexed when the stationary and movable contacts are in engagement. This flexure is advantageous in that the switch contacts are thus held together by resilient means and prevented from chattering.

From the foregoing it will be seen that the means embodied in the present construction afford the advantages particularly desired in a snap action switch, namely that the actuatable means are practically free of friction, that good contact pressure is maintained up to the point of snap over with the result that chattering-of the contacts is avoided, and that the contactor element may be made from a single punching greatly simplifying manufacturing insuring uniformity of parts.

While I have shown a preferred embodiment of my invention, many changes may be made in carrying out thisconstruction without departing from the principles of the invention, and the appending claims are contemplated to cover such modifications as are within the spirit and scope of the invention.

I claim as my invention:

1. An electric switch comprising means movable back and forth in a fixed path between two positions to cause engagement and disengagement of a movable contact with a stationary contact, a

contact spring engaging said means and arranged to shift said means to either position by tilting said spring, a movable actuating spring, arranged between a support and said contact spring at its end opposite said means, to maintain said contact spring under compression in either position and deflectable between said support and said contact spring to maintain the compression of said contact spring to keep said contacts in engagement and store energy to tilt said contact spring to disengage said contacts after said actuating spring is moved a predetermined distance and suflicient energy has been stored therein to counterbalance the expansion or said contact spring, and an actuator applied to the actuating spring intermediate its ends to deflect said actuating spring.

2. A switch comprising a movable contact engageable with a stationary contact, a contact carrier movable in a fixed path carrying said movable contact and shiftable to opposite positions to engage and disengage said contacts, a contact spring engaging said carrier and arranged to shift said contact carrier to either position by tilting said spring, a movable actuating spring, arranged between a support and said contact spring at its end opposite the contact; carrier, to maintain said contact spring under compression in either position, and deflect'able between said support and said contact spring to maintain the compression of said contact spring to keep said contacts in engagement and store energy to tilt said contact spring to disengage said contacts after said actuating spring is moved a predetermined distance and suflicient energy has been stored therein to counterbalance the expansion of said contact spring, and an actuator applied to the actuating spring intermediate its ends to deflect said actuating spring.

3. In an electrical switch having a stationary contact and a movable contact engageable therewith, means for actuating the movable contact with a snap motion into and out of engagement with the stationary contact, comprising a pair of flat spring members, both rigidly mounted at one end in edgewise side by side relation, one member of which is longer than the other, the longer member carrying the movable contact, and an expansion spring confined between opposing adjacent end portions of said members to yieldingly urge the same apart, so that the combined spring action of the shorter spring member and the expansion spring at all times yieldingly urges the longer spring member toward one side or the other. of a plane coinciding with the common I plane of the end mounting of said members, and an actuator applied to the shorter spring member intermediate its ends to deflect said shorter spring member.

4. In a snap action switch, the combination comprising a contact carrier mounted to be deflected to and from a contact, and having a free end movable about a fixed end, an endwise compressible resilient expansion member engaging said carrier at a point remote from the fixed end thereof, a laterally deflectable member with resiliency to lateral forces having a fixed end near the fixed end of said contact carrier, and having a free end engaging the end of said resilient expansion member opposite the end thereof engaged by said contact carrier, and means to apply force to said laterally deflectable member intermediate its ends to urge it toward a line joining the fixed end of said laterally deflectable member and the point of engagement between said resilient expansion member and said carrier! 5. In a snap action switch; the. combination comprising a contact carrier composed of flat spring material, mounted to bedeflected to and from a contact, and having a free end and rigidly mounted end, an endwise compressib e resilient expansion member enga in said carrier at a point remote from the rigid mounting thereof, a laterally deflectable member composed of flat spring material rigidly mounted near the rigid mounting of said carrier, and having a free end engaging the end of said resilient expansion member opposite the end thereof engaged by said contact carrier, and means for acting upon said laterally deflectable member intermediate its ends to deflect and urge the same toward a line joining the rigid mounting of said laterally deflectable member and the point of engagement between said resilient expansion member and said carrier. I

6. In a snap action switch, a contactor element comprising a punching of spring material,

said punching'having a cut-out forming a contactor arm and a spring arm, one disposed within the other and extending in the same direction from a common base, an expansion spring having one of its ends seated on the spring arm and the other seated on the contactor arm, whereby said arms are biased with respect to each other and an actuator applied to said spring arm intermediate its ends to deflect said spring arm.

7. In an electrical switch, a combined mounting and actuating member for a movable contact, comprising a flat spring blade having a substantially U-shaped cut-out therein so as to provide substantially two independent spring blades, one longer than the other with the shorter blade disposed within the longer, the longer blade carrying the movable contact adjacent to its portion defining the closed end of the U-shaped cut-out, and an expansion spring having one of its ends seated on the longer blade and the other of its ends seated on the shorter blade, whereby said arms are biased with respect to each other and an actuator applied to said shorter blade intermediate its ends.

8. In a snap action switch, a contactor element comprising a punching of spring material, said punching having a cut-out whereby to form a contactor arm and a spring arm, one disposed within the other and extending in the same direction from a common base, a tip forming the apex of the spring arm and a tip forming the apex of the opposing edge of the contactor arm, an expansion spring, cup bearings on each end of said expansion spring, one of said bearings being seated on the tip of the spring arm and the other of said bearings being seated on the tip of the contactor arm, the spacing of said bearing points being such as to place the spring under compression, whereby said arms are biased with respect to each other and an actuator applied to said spring arm intermediate its ends.

9. In a snap action switch, a contactor element adapted to be supported in cantilever fashion at one of its ends and composed of apair of flat spring members one longer than the other, said members being divergent with respect to each other in unstressed condition, an expansion spring confined between the free ends of said members, an actuator arranged to apply pressure to the short arm intermediate its ends to deflect the short arm, said bias of said divergent short member being greater than any opposing forces developed in the expansion spring, whereby, the return of said short member is assured upon removal of actuating pressure applied thereto.

10. In a switch, the combination comprising a contact carrier movable back and forth between two positions and having a free end movable about a fixed end, an endwise compressible resilient expansion member engaging said carrier at a point remote from the fixed end thereof; a laterally deflectable member having a fixed end near the fixed end of said contact carrier and being laterally biased therefrom when in its unstressed position, the free end of said biased member engaging the end of said resilient expansion member opposite the end thereof engaged by said contact carrier and said biased member being flexible intermediate its ends to store suflicient energy to cause said contact carrier to move to a second position and an actuator arranged to flex said biased member to store said sufiicient energy and whereby on retraction of said actuator, the contact carrier is caused to move back to its original position.

11. In an electrical switch having a pair of oppositely disposed stationary contacts and a movable contact juxtapositioned therewith, means for actuating the movable contact with a snap motion into and out of engagement with the stationary contacts, comprising an element composed of spring material and formed of two arms adapted to be supported in cantilever fashion from a common base, one of said arms being disposed within the other and each capableof cutting the longitudinal plane of the other, the outer arm mounting the movable contact, the inner arm being appreciably shorterthan the outer arm and in its unstressed condition inclined at an angle to the longitudinal axis of the outer arm, and an expansion spring confined between the free end portions of said arms, and an actuator arranged to apply pressure to the inner arm intermediate its ends to cause the outer arm to move from one closed position to the other closed position with a snap motion.

12. A snap acting control mechanism comprising the combination with a member movable in a fixed path between two positions and an expansion spring engaging said member and arranged to maintain said member in one position and to shift and maintain said member to the other position by tilting of said spring, of an actuating means including a fixed end and an opposite end arranged to be movable about said fixed end, a resilient member mounted between the said ends with the movable end of said actuating means connected to said expansion spring, said resilient member arranged to be deflected laterally of a line joining said two ends and between said two ends, and an actuator to deflect and store energy in said resilient member to overcome the reactive force of the expansion spring to move said member into its other position with a snap motion.

13. A snap acting control mechanism comprising in combination, a first member having a free end movable in a fixed pathbetween two positions, an actuating means having a free end movable in a fixed path between two positions, and a resilient expansion member spaced between and engaging the said two free ends to form a resilient connection therewith having an axis of maximum stress, said first member and said ac-' tuating means arranged to allow said expansion member to move to alternate positions of reduced stress with snap action, and said actuating means including a resilient member and an actuator, said latter resilient member to be intermediate the actuator and the free end of said actuating means and arranged to be deflected in a direction across the said axis of maximum stress, whereby, upon motion of the actuator energy is stored in the latter resilient member to initiate snap action in said expansion member from one position to the alternate position before the movable end of the actuating means reaches said axis of maximum stress.

14. A snap acting control mechanism comprising in combination, a first member having a free end movable in a fixed path between two positions, an actuating means having a free end movable in a fixed path between two positions, and a resilient expansion member spaced between and engaging the said two free ends to form a resilient connection therewith having an axis of maximum stress, said first member and said actuating means arranged to allow said expansion member to move to alternate positions of reduced stress with snap action, and said actuating means including a resilient member and an actuator, said latter resilient member to be intermediate the actuator and the free end of said actuating means andarranged to be deflected in a direction across thesaid axis 01' maximum stress, whereby, upon motion of the actuator energyi's stored in the latter resilient member to cause snap action in said expansion member from one position to the alternate position.

' GUSTAV O. WILMS. 

